Big bangs theory blames lava fields for mass extinctions

Vast sheets of prehistoric lava that oozed across the land millions of years ago were probably caused by meteorites slamming into the Earth's crust, scientists say.

The lava sheets, 10 of which have been discovered around the world, coincide with mass extinctions, suggesting the huge volumes of magma caused global changes in climate that made Earth inhospitable to all but the hardiest species.

The largest lies in Siberia, is roughly the size of Thailand and dates back 252 million years. "We think lava poured on to Siberia for between 100,000 and one million years, leaving the surface covered with four million cubic kilometres of lava," said Linda Elkins-Tanton, a geologist at Brown University, Rhode Island.

Another sheet, discovered in western India and known as the Deccan flood basalt, is believed to have formed 66 million years ago. Both, like the others around the world, are largely overgrown but in places the lava is still visible. Until now, their origins have been a mystery. Dr Elkins-Tanton and Bradford Hager at Massachusetts Institute of Technology decided to investigate whether meteorites would have enough energy to release the amounts of lava contained in the sheets.

In a paper to be published in next month's issue of Earth and Planetary Science Letters, they show that a meteorite with a diameter of less than a mile could dent the Earth's crust enough to weaken it, allowing molten lava as hot as 1,300C (2,372F) to pierce through. "Our computer models show this is absolutely possible. It ties into some of the most exciting mysteries of life on Earth," said Dr Elkins-Tanton.

The researchers believe that the lava may have released large amounts of carbon dioxide as it spilled out over land. That in turn would lead to a runaway greenhouse effect, making life on Earth more like life on Venus, causing a huge rise in temperatures.

About half of the lava sheets discovered have been dated to match the timing of mass extinctions, suggesting they may have played a significant part in wiping species out on a devastating scale. "It has deep ramifications for life on Earth. There's no reason it couldn't happen again," said Dr Elkins-Tanton.